The helicopter was observed in forward flight at low altitude and also in a nose-down spiralling descent before it disappeared from sight and hit the ground. This descent profile, and the confined tree damage at the accident site, is indicative of uncontrolled flight. There was a road about 275 feet from the impact site. The pilot would have chosen the road before the trees had an emergency or precautionary landing been initiated. Since there is no evidence of mechanical failure that would explain the transition from a controlled, level flight to the steep, nose-down descent, the analysis will focus on what other unanticipated event could have been a factor in this occurrence. Normally, as collective is introduced at take-off, the pilot monitors the power turbine speed and uses the collective mounted governor trim switch (beep switch) to maintain power at 100%. If the throttle was rolled full open at take-off there could be a slight rotor rpm drop during climb out; however, the fuel control/governor would sense the drop, increase the fuel schedule and restore the rpm. The throttle would have to be set considerably off the full open position before the rotor rpm would drop to a value so low that control of the helicopter could not be maintained. This condition would not be expected during the blade strobing procedure until the latter stages, when a simulated autorotation is carried out to confirm that rotor rpm remains within a specific range. This (autorotation) check would, however, normally be initiated later in the flight profile, at a safe altitude and over the airport rather than at the time and area associated with the accident. The rotor blade damage observed at the accident site was consistent with low rpm at impact, and the power turbine and rotor rpm instrument readings were captured at low rpm values. No mechanical deficiencies were identified that would have caused the rotor rpm to decay in flight. Possible reasons for these conditions are that the pilot may have increased collective pitch in an attempt to reduce the descent rate just prior to impact with the ground or he may have rolled off the throttle just before hitting the trees. Although the left seat dual control sticks had been removed in preparation for the maintenance related flight, protective covers had not been installed over the stub shafts. Also, the anti-torque pedals just forward of the left crew seat position remained installed. During blade strobing on a maintenance flight, the AME would normally rest the test equipment on his lap or place it on the floor between his feet when making notes. The test equipment includes lengths of electrical cord for power supply and equipment operation. It is possible that the equipment or cord could have fallen on, or become entangled in, the exposed flight control stub shafts or the anti-torque pedals, thereby restricting pilot input to those controls. However, the probability that this contact would initiate the loss of helicopter control is considered unlikely. The pilot would be resting his feet on the anti-torque pedals and his hands would be on the cyclic and collective control levers. Any force applied to the control lever stub shafts or anti-torque pedals by this method would be felt by the pilot and easily opposed. A distraction-causing event, such as the strobing equipment or the note pad falling off the AME's lap during the flight, and a subsequent attempt to grab the falling item, might have led to a leg being unintentionally extended and striking one of the anti-torque pedals with sufficient force to initiate a severe yaw. Information gathered from past occurrences has indicated that the helicopter would roll towards inverted if an abrupt input to the anti-torque pedals was applied. The roll rate would be greatest at high airspeeds, and if the helicopter was configured on fixed floats. A loss of control at low altitude would provide little time for the pilot to arrest the descent before striking the ground. The fracture to the pilot's lower right leg is a possible indication that he was applying considerable force on the right anti-torque pedal. Hard right pedal input would be a recovery response to regain directional control.Analysis The helicopter was observed in forward flight at low altitude and also in a nose-down spiralling descent before it disappeared from sight and hit the ground. This descent profile, and the confined tree damage at the accident site, is indicative of uncontrolled flight. There was a road about 275 feet from the impact site. The pilot would have chosen the road before the trees had an emergency or precautionary landing been initiated. Since there is no evidence of mechanical failure that would explain the transition from a controlled, level flight to the steep, nose-down descent, the analysis will focus on what other unanticipated event could have been a factor in this occurrence. Normally, as collective is introduced at take-off, the pilot monitors the power turbine speed and uses the collective mounted governor trim switch (beep switch) to maintain power at 100%. If the throttle was rolled full open at take-off there could be a slight rotor rpm drop during climb out; however, the fuel control/governor would sense the drop, increase the fuel schedule and restore the rpm. The throttle would have to be set considerably off the full open position before the rotor rpm would drop to a value so low that control of the helicopter could not be maintained. This condition would not be expected during the blade strobing procedure until the latter stages, when a simulated autorotation is carried out to confirm that rotor rpm remains within a specific range. This (autorotation) check would, however, normally be initiated later in the flight profile, at a safe altitude and over the airport rather than at the time and area associated with the accident. The rotor blade damage observed at the accident site was consistent with low rpm at impact, and the power turbine and rotor rpm instrument readings were captured at low rpm values. No mechanical deficiencies were identified that would have caused the rotor rpm to decay in flight. Possible reasons for these conditions are that the pilot may have increased collective pitch in an attempt to reduce the descent rate just prior to impact with the ground or he may have rolled off the throttle just before hitting the trees. Although the left seat dual control sticks had been removed in preparation for the maintenance related flight, protective covers had not been installed over the stub shafts. Also, the anti-torque pedals just forward of the left crew seat position remained installed. During blade strobing on a maintenance flight, the AME would normally rest the test equipment on his lap or place it on the floor between his feet when making notes. The test equipment includes lengths of electrical cord for power supply and equipment operation. It is possible that the equipment or cord could have fallen on, or become entangled in, the exposed flight control stub shafts or the anti-torque pedals, thereby restricting pilot input to those controls. However, the probability that this contact would initiate the loss of helicopter control is considered unlikely. The pilot would be resting his feet on the anti-torque pedals and his hands would be on the cyclic and collective control levers. Any force applied to the control lever stub shafts or anti-torque pedals by this method would be felt by the pilot and easily opposed. A distraction-causing event, such as the strobing equipment or the note pad falling off the AME's lap during the flight, and a subsequent attempt to grab the falling item, might have led to a leg being unintentionally extended and striking one of the anti-torque pedals with sufficient force to initiate a severe yaw. Information gathered from past occurrences has indicated that the helicopter would roll towards inverted if an abrupt input to the anti-torque pedals was applied. The roll rate would be greatest at high airspeeds, and if the helicopter was configured on fixed floats. A loss of control at low altitude would provide little time for the pilot to arrest the descent before striking the ground. The fracture to the pilot's lower right leg is a possible indication that he was applying considerable force on the right anti-torque pedal. Hard right pedal input would be a recovery response to regain directional control. The pilot and the AME were certified and qualified for the flight in accordance with existing regulations. The aircraft weight and centre of gravity were within limits. Records indicate that the aircraft was certified, equipped, and maintained in accordance with existing regulations and approved procedures. There was no evidence of any pre-impact mechanical or structural failure. The ELT was found buried in the ground and had not activated. The switch was in the OFF position, and there was no evidence that it had been armed before the flight. The engine was operating at impact and power was being transmitted to the main and tail rotors. The power turbine (N2) rpm was 73% and the main rotor rpm (Nr) was 67% at impact. The damage observed on the rotor blades was consistent with low rotor rpm at impact. The descent profile observed by the witness and the accident site tree and ground damage was consistent with an uncontrolled descent. Abrupt helicopter attitude changes due to inappropriate anti-torque pedal input have been documented in past occurrences. The dual control sticks (cyclic and collective) were removed before the maintenance flight, but the stub shaft protective covers were not installed and the left seat dual anti-torque pedals remained installed. The test equipment is normally held on the AME's lap or placed on the floor between his feet and is in close proximity to the anti-torque pedals. The equipment also includes sufficient lengths of cord that contact with the pedals or stub shafts is possible. The pilot had a compound fracture of the lower right leg, a possible indication that he was applying hard right pedal at the time of impact. Right pedal input is a possible indication that the pilot was attempting to regain directional control of the helicopter.Findings The pilot and the AME were certified and qualified for the flight in accordance with existing regulations. The aircraft weight and centre of gravity were within limits. Records indicate that the aircraft was certified, equipped, and maintained in accordance with existing regulations and approved procedures. There was no evidence of any pre-impact mechanical or structural failure. The ELT was found buried in the ground and had not activated. The switch was in the OFF position, and there was no evidence that it had been armed before the flight. The engine was operating at impact and power was being transmitted to the main and tail rotors. The power turbine (N2) rpm was 73% and the main rotor rpm (Nr) was 67% at impact. The damage observed on the rotor blades was consistent with low rotor rpm at impact. The descent profile observed by the witness and the accident site tree and ground damage was consistent with an uncontrolled descent. Abrupt helicopter attitude changes due to inappropriate anti-torque pedal input have been documented in past occurrences. The dual control sticks (cyclic and collective) were removed before the maintenance flight, but the stub shaft protective covers were not installed and the left seat dual anti-torque pedals remained installed. The test equipment is normally held on the AME's lap or placed on the floor between his feet and is in close proximity to the anti-torque pedals. The equipment also includes sufficient lengths of cord that contact with the pedals or stub shafts is possible. The pilot had a compound fracture of the lower right leg, a possible indication that he was applying hard right pedal at the time of impact. Right pedal input is a possible indication that the pilot was attempting to regain directional control of the helicopter. The helicopter was observed in an uncontrolled descent from low altitude when it hit the ground. The cause of the uncontrolled descent could not be determined; however, in the absence of any evidence of mechanical or structural failure prior to impact, it is considered that the loss of control was likely a result of unintentional flight control input.Causes and Contributing Factors The helicopter was observed in an uncontrolled descent from low altitude when it hit the ground. The cause of the uncontrolled descent could not be determined; however, in the absence of any evidence of mechanical or structural failure prior to impact, it is considered that the loss of control was likely a result of unintentional flight control input. Helico Air Service Limited has implemented a policy to ensure that all dual controls are removed and protective covers installed prior to flight.Safety Action Taken Helico Air Service Limited has implemented a policy to ensure that all dual controls are removed and protective covers installed prior to flight.